A data center is a central data processing facility and/or the group of people who manage the data processing and networks of a commercial or government entity. A data center may contain a network operations center (NOC), which is a restricted access area containing automated systems that constantly monitor server activity, Web traffic, and network performance and report even very slight irregularities to engineers so that they can spot potential problems before they happen. A data center may also house Web servers and/or provide data serving and other services for other companies.
An interruption in power to the data center (e.g., a blackout or brownout) may result in an interruption in services by the data center or a catastrophic data loss. To prevent this, many data centers and telephone networks use an un-interruptible power supply (UPS) to provide back-up power during power interruptions and/or to provide enough power to allow these systems to shut down in a known state. Typically, a component likely to fail in a UPS system is the battery or batteries which supply the back-up power. Because the batteries are coupled in series in a typical UPS system, the failure of one battery can cause the premature failure of the entire UPS when back-up power is required. Therefore, it is important to monitor the condition of the batteries to insure that the UPS is in condition to provide power during an emergency.
FIG. 1A shows an exemplary prior art UPS system 100. Alternating current (AC) power is received via coupling 110 and is input to a rectifier circuit 120. Rectifier circuit 120 converts the AC power to a direct current (DC) or constant voltage which is output to coupling 121. Some of the DC voltage goes to inverter circuit 130 which converts the DC voltage to an AC voltage which is supplied to the data center via coupling 131. A portion of the DC voltage from rectifier circuit 120 is directed to battery string 140 via coupling 141 and recharges the batteries so that they are available to supply power as needed. During a power interruption, when power via coupling 110 is unavailable or reduced, the batteries in battery string 140 discharge and immediately supply power to inverter circuit 130 via coupling 141 where the DC voltage is converted to an AC voltage to supply power to the data center via coupling 131.
FIG. 1B shows an exemplary battery string 140 used in a conventional UPS system. A typical battery string 140 comprises a plurality of batteries (e.g., batteries 140a, 140b, 140n) which are coupled in series. In a conventional UPS system, a battery string may comprise as many as 30–40 batteries. Additionally, a conventional UPS system may use a single battery string, or multiple strings (e.g., as many as 5 battery strings) in parallel to provide back-up power.
In one type of conventional battery monitoring system, a voltage monitor circuit (e.g., voltage monitors 150a, 150b, 150n of FIG. 1B) is respectively coupled with each battery in the UPS system and may also be coupled with a monitoring unit (e.g., monitoring unit 160 of FIG. 1B) via signal pathways 170, 171, and 172. The voltage monitor may be used to directly measure the impedance of its respective battery and, when the impedance exceeds a pre-determined level, generates an alarm signal to the monitoring unit.
This type of monitoring system is expensive to establish and maintain for many users because of the expense of the plurality of voltage monitor string 150 and the associated plurality of signal pathways needed to couple each voltage monitor with monitoring unit 160. Often, the cost of this type of monitoring system is as much as the battery string and UPS itself.
A less expensive monitoring system couples a current probe to the electrical coupling between the batteries in the battery string. The current probe monitors the current flux, also known as “ripple current” which is electrical noise generated at the rectifier circuit (e.g., rectifier circuit 120 of FIG. 1). A typical current probe comprises an AC current transformer having an iron core. During the cycle of an AC waveform, the iron core of the current probe becomes magnetized as the waveform approaches its peak. The iron core then becomes de-magnetized as the waveform approaches its trough. Unfortunately, during a power interruption, the iron core cannot de-magnetize and may begin to heat, which can cause a failure of the current probe. Thus, the current probes currently used may fail after a power interruption and therefore need to be replaced. This system also requires periodic maintenance wherein a technician checks the monitoring device 160 to determine if a battery failure has occurred. These periodic visits may be costly and unnecessary unless a battery failure has actually occurred.
Additionally, because of irregularities in the power supply (e.g., a temporary drop in the supply voltage) the batteries of the UPS may discharge to provide a constant supply of power. These occasional discharges of the battery string have a cumulative affect on the effective life of the current probe. Thus, over time the current probe approach can possibly fail to report a battery failure of the UPS. Additionally, these current probes are not coupled with a monitoring system. In other words, a technician is required to occasionally make a reading of the current probe to determine the status of the battery string.